Uranium
}} Uranium is a weakly radioactive element number 92 with the symbol '''U. It is silvery-gray actinide metal in pure form, though it reacts with air to form a dark oxide coating. Most uranium occurs as uranium-238, with a small percentage appearing as the fissile uranium-235, both of which decay via emitting alpha particles. Unlike ordinary uranium, dao-influenced uranium is slightly more stable and also more prevalent in the environment, both due to the increased stability and also from increased production during stellar nucleosynthesis. It has various usages, such as fuel for nuclear fission reactors and nuclear bombs, as well as uses based off of its high density, such as armor and weaponry. Characteristics Physical When in refined form, uranium is a silver-gray, weakly radioactive metal that is malleable, ductile, paramagnetic and a poor conductor of electricity. It has a very high density, denser than lead, though it is less dense than tungsten and gold. It has 3 allotropes, the α phase has an orthorhombic crystal structure and is stable up to around 660°C, the β state is tetragonal and is stable from 660°C to 760°C, and the γ state has a body-centered cubic structure and is stable from 760°C to the melting point. The gamma state is the most malleable and ductile of the three. Chemical Uranium reacts with most non-metallic elements and compounds aside from the noble gases, and if it has been finely divided it will react with cold water or ignite on its own in air. Oxidizing acids will dissolve uranium, though non-oxidizing acids with the exception of hydrochloric acid will only slowly attack it. Atomic Uranium has an electron configuration of Ra]5f36d17s2, the reason for the electron in the 6d shell instead of the 5f shell is due to the similarity of energies between the 5f, 6d and 7s shells. It is possible for uranium to lose all 6 of its valance electrons, leaving behind an inert core of inner electrons, however it is also possible that it only loses some of its valence electrons, entering a lower oxidation state. The 7s and 6d electrons are the first to be lost, with the U3+ ion having an Ra5f3 state. Isotopes Both uranium-235 (found naturally) and uranium-233 (prepared by bombarding thorium with neutrons) are fissile, which means that they can sustain a fission chain reaction and can be used to generate power (or to create a nuclear bomb). Other isotopes are fissionable, meaning that they can release energy by being fission, but will not sustain a fission chain reaction. Uranium-238 is the most stable and plentiful isotope with a half life of 7.35 billion years, (98.45% of natural uranium) while uranium-235 is the second most stable isotope with a half life of 757 million years (1.55%). Occurrence Compounds Oxides Uranium forms several different oxides including uranium monoxide (UO), uranium dioxide (UO2), uranium trioxide (UO3), diuranium pentoxide (U2O5), uranium peroxide (UO4·2H2O), and triuranium octoxide (U3O8), where U3O8 and UO2 are the most common forms. Both of these oxides are relatively stable over a wide range of environmental conditions, though UO2 will slowly convert to U3O8 at ordinary temperatures. Halides Various fluorides of uranium exist such as UF3, UF4, UF5 UF6 and various intermediate fluorides. UF6 is a volatile and reactive white solid, and is the most volatile known compound of uranium. UCl3, UCl4, UCl5, UCl6, UBr3, UBr4, UI3, UI4 are also known to exist, though they are less stable than the fluorides and react with air or water. Mixed oxyhalides are also known, they are water-soluble and their stability decreases as the mass of the halide increases. Organometallic Organouranium compounds are not stable, and only a few such compounds, such as uranocene, exist. Attempts to create uranium carbonyls by exposing uranium to carbon monoxide instead result in the production of uranium carbide. Other Compounds Uranium forms hydrides when uranium is heated in the presence of hydrogen, this property is used to form additional uranium compounds starting from the uranium hydrides. Uranium forms several nitrides and carbides, which are relatively inert semimetallic compounds that react with water and which can burn in air to form U3O8. The carbides can be made by either adding carbon to molten uranium or by exposing uranium to carbon monoxide at high temperatures, forming UC and UC2. Additionally, U2C3 can be made by heating a mixture of UC and UC2 and exposing it to mechanical stress. Uranium nitrides can be formed by simply exposing the metal to nitrogen and include UN, UN2, and U2N3. Aqueous chemistry Various salts of many oxidation states of uranium are soluble, with typical forms being U3+ (purple), U4+ (green), (pink), and (yellow). Unlike the uranium-oxide cations, the uranium-oxide anions are generally not water-soluble. Applications Exposure and toxicity